Cover for secondary battery

ABSTRACT

By using a rivet which serves also as a terminal member, and a sealing member which serves also as an insulating member, a terminal member and an insulating member can be omitted, thereby forming the lid from only three parts i.e. the body, rivet and sealing member. The sealing member includes a cylindrical portion and a flange portion which are separate members. The cylindrical portion is formed by cutting a fluororesin tube. The flange portion is formed by punching a polypropylene resin sheet. Thus, the number of parts can be reduced to four, so that it is possible to reduce the parts cost and manufacturing cost compared to conventional lids.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a secondary battery, and particularly to an improved type which can be manufactured inexpensively.

[0002] Spreading of cellular phones is an eye-opener. As power sources of such cellular phones, lithium ion batteries are typically used in place of nickel-cadmium batteries and nickel-hydrogen batteries.

[0003] Since lithium ion batteries are higher in the working voltage and large in the energy capacity compared to nickel-cadmium batteries, they are durable and have such electrical properties that they are less likely to deteriorate due to additive charging. Further they are lightweight. Due to these facts, they are advantageous for use in light, thin, short and small devices such as cellular phones and video cameras.

[0004] But, while lithium ion batteries have the above-described advantages, problem is that they are expensive.

[0005] An object of this invention is to provide a lithium ion battery which is less expensive than conventional.

SUMMARY OF THE INVENTION

[0006] In order to solve the above object, in this invention, the structure of a lid of a lithium ion battery has been improved so that it can be manufactured at a low cost to reduce the cost of the entire lithium ion battery. First, referring to FIGS. 2 and 3, the structure of the lid of a conventional square-shaped lithium ion battery will be described.

[0007] The lid 10 of the square-shaped lithium ion battery shown in FIG. 2 has a body 1 formed of an iron plate plated with aluminum or nickel, and has a rectangular shape corresponding to the shape of a housing on which it is placed. To the center of the body 1, a rectangular terminal member 2 for mounting a lead wire is joined by a rivet 5 through a sealing member 4 together with an insulating member 3 slightly bigger than the terminal member 2. In the figures, thin-wall portions 6 of the body 1 function as a safety valve if the internal pressure of the housing rises. A hole 7 is provided to pour an electrolyte.

[0008] Next, a combined form of these parts of the lid 10 is described with reference to FIG. 3 which is an exploded perspective view.

[0009] As shown in FIG. 3, at the center of the body 1, a hole 1 a for mounting the terminal member 2 and the insulating member 3 is formed. Through holes 2 a and 3 a are also formed in the center of the terminal member 2 and the insulating member 3, respectively, to mount them to the body 1.

[0010] The sealing member 4 for mounting the terminal member 2 and the insulating member 3 is a cylinder having an outward flange 4 a at one end thereof. A cylindrical portion 4 b has such an outer diameter as to be fitted in the mounting hole 1 a at the center of the body 1. The sealing member 4 is formed by injection-molding a polypropylene resin. Such members are mounted to the body 1 in the manner described below.

[0011] First, as shown in FIG. 3, the terminal member 2 and the insulating member 3 are superposed with the insulating member under so that the centers of their through holes 2 a and 3 a will align. Then they are placed on the body 1 with the centers of the through holes 2 a, 3 a of these members 2, 3 aligned with the center of the mounting hole 1 a at the center of the body 1.

[0012] Next, the cylindrical portion 4 b of the sealing member 4 is inserted into the through holes 1 a, 2 a and 3 a of the three members from the back of the body 1. The rivet 5 is then inserted into the cylindrical portion 4 b of the sealing member 4 from the back of the body 1 and joined by caulking. Now the cover 10 is in the state shown in FIG. 2.

[0013] A lead wire (not shown) is mounted by welding to the surface of the terminal member 2, which has thus been mounted to the body 1. In order to ensure welding, as the terminal member 2, one having an area having a large occupying rate relative to the body 1 as shown in the figure was needed.

[0014] But due to advancement of the welding technology, it became possible to reduce the required area to be welded to a value substantially equal to the area of the end face of the rivet 5 after caulking.

[0015] Thus, by using the rivet 5 as the terminal and welding lead wire to the rivet, the terminal member 2 can be omitted. This makes it possible to manufacture the lid 10 at a low cost due to the reduction in the number of parts.

[0016] Thus, in this invention, the rivet 5 is also used as the terminal member 2 to reduce the number of parts to four.

[0017] Further, by making the sealing member 4 of an insulating material and using it also as the insulating member 3, it is possible to further reduce the number of parts to three (see FIGS. 1B and 1C).

[0018] Moreover, according to this invention, the sealing member 4 may consist of a cylindrical portion 4 b and flange portion 4 a (FIGS. 1A and 1B). Advantages of this arrangement will be described below.

[0019] Heretofore, the insulating member 3 was, as described above, formed by injection molding of inexpensive polypropylene resin. But if the housing is made thin to reduce the size (thickness) of the battery, influence of heat produced in welding the housing and the lid 10 together increases, so that the propropylene resin, which is inferior in heat resistance, cannot withstand the heat. Thus, it was impossible to reduce the size. Instead of polypropylene resin, using a fluororesin, which is superior in heat resistance, is considered.

[0020] But a fluororesin is not only expensive but is also difficult to injection mold, so that in order to perform injection molding, special grade one has to be used. Thus, the cost is high compared with other materials.

[0021] In this invention, the sealing member 4 comprises the cylindrical portion 4 b and the flange portion 4 a, which are separate from each other and simple in shape.

[0022] With this arrangement, disks for such simply shaped cylindrical portion 4 b and flange portion 4 a can be manufactured by punching or extruding a sheet material. Such work is inexpensive in cost. Thus, a fluororesin may be used, which is expensive but superior in heat resistance, it is possible to obtain a product more inexpensive than conventional in the end.

[0023] Also, in the entire sealing member 4, the flange portion 4 a is a portion for which high sealability is not required as for the cylindrical portion 4 b but insulating properties are mainly required. Thus, even if it is deformed under the influence of heat buildup during welding, this will pose no big problem. Thus, this portion may be formed, not from an expensive fluororesin, but from a sheet member of inexpensive polypropylene resin by inexpensive punching. This further reduces the manufacturing cost.

[0024] The above description has been made with reference to a lithium ion battery. But this invention is not limited to lithium ion batteries but is applicable to other secondary batteries such as nickel-cadmium batteries and nickel-hydrogen batteries if the lid has the same structure for the connection of lead wires.

[0025] Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIGS. 1A, 1B and 1C are sectional views of lids of first, second and third embodiments;

[0027]FIG. 2A is a plan view of a conventional lid;

[0028]FIG. 2B is a sectional view of the same; and

[0029]FIG. 3 is an exploded perspective view of the conventional lid.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] Hereinbelow, referring to the drawings, the embodiments of this invention will be described. For parts identical to those of the conventional lid, identical numerals are used and their description is omitted. In the figures, lead wires connected to the lid are not shown.

First Embodiment

[0031] The embodiment shown in FIG. 1A is a lid 10 having a conventional terminal member 2 and an insulating member 3. But the sealing member 4 has the cylindrical portion 4 b and a flange portion 4 a formed separately from each other.

[0032] For the cylindrical portion 4 b for which sealability is especially required, a fluororesin is used which is, though expensive, superior in heat resistance and is less likely to be deformed even when exposed to heat buildup during welding. It may be formed by cutting a tube made therefrom.

[0033] On the other hand, the flange portion 4 a for which insulating properties are mainly required but slight deformation is permitted, is formed from an inexpensive polypropylene by punching a sheet member formed therefrom into a doughnut-shaped disk.

[0034] Because for both the cylindrical portion 4 b and flange portion 4 a, ready-made resin tubes and plates are used without using a complicately shaped molds, it is possible to manufacture them at a lower cost than a sealing member 4 having the cylindrical portion 4 b and flange portion 4 a integral with each other.

Second Embodiment

[0035] In the embodiment shown in FIG. 1B, by using the rivet 5 which serves also as the terminal member 2, and the sealing member 4 which serves also as the insulating member 3, the terminal member 2 and insulating member 3 are omitted to form the lid 10 from only three parts, i.e. the body 1, solid rivet 5 and sealing member 4.

[0036] For the sealing member 4, as with the first embodiment, the cylindrical portion 4 b and flange portion 4 a are formed as separate elements. The cylindrical portion 4 b is formed by cutting a fluororesin tube, and the flange portion 4 a is formed by punching a polypropylene sheet member.

[0037] Since this embodiment has no terminal member 2 or insulating member 3, the parts cost and manufacturing cost are less expensive.

Third Embodiment

[0038] In the embodiment shown in FIG. 1C, instead of splitting the sealing member 4 into the cylindrical portion 4 b and flange portion 4 a as in the second embodiment, an integral one is used, which is formed by injection molding.

[0039] By this arrangement, the number of parts is smaller than in the second embodiment, and can be reduced to only three i.e. the lid body 1, rivet 5 and sealing member 4. Assembly is thus simplified.

[0040] But since a complicated shape having the cylindrical portion 4 b and flange portion 4 a integral with each other cannot be manufactured by extrusion molding, it is formed by injection molding. As described above, in this method, instead of using a fluororesin, which pushes up the cost, a polypropylene is used.

[0041] Thus, since a polypropylene resin is inferior in heat resistance to a fluororesin, in order that heat can be dispersed to the surroundings, this embodiment is applicable to one in which the lid body 1 has larger dimensions such as width and length compared with the second embodiment.

[0042] The structure of the lid 10 of each embodiment is, as described above, applicable to a nickel-cadmium battery, nickel-hydrogen battery or any other secondary battery. In view of the structure thereof, they can also be manufactured less expensively than conventional.

[0043] In this invention, since the lid of a secondary battery is structured as above, the secondary battery can be manufactured at a lower cost than conventional. 

What is claimed is:
 1. A lid of a secondary battery, said lid comprising a plate-shaped body formed with a hole, a terminal member and an insulating member superposed on a peripheral edge of the hole formed in said body with said insulating member arranged under said terminal member, a cylindrical sealing member having a flange portion at one end thereof and inserted in said hole, and a rivet inserted in said sealing member and caulked to join said terminal member and said insulating member to said body, characterized in that: said sealing member comprises a flat plate having a hole to form said flange portion, and a cylindrical portion that is separate from said flange portion.
 2. A lid of a secondary battery as claimed in claim 1 wherein said cylindrical portion is made of a fluororesin.
 3. A lid of a secondary battery, said lid comprising a plate-shaped body formed with a hole, an insulating member mounted in said hole formed in said body, a cylindrical sealing member having a flange portion at one end thereof and inserted in said hole, a rivet inserted in said sealing member and caulked to join said insulating member and said sealing member to said body, and a lead wire mounted to one end face of said rivet.
 4. A lid of a secondary battery comprising a plate-shaped body formed with a hole, a cylindrical sealing member inserted in said hole formed in said body, said sealing member having a flange portion at one end thereof and made of an insulating material, a rivet inserted in said sealing member and caulked to join said sealing member to said body, and a lead wire mounted to one end face of said rivet.
 5. A lid of a secondary battery as claimed in claim 3 or 4 wherein said sealing member is made of a fluororesin.
 6. A lid of a secondary battery as claimed in claim 3 or 4 wherein said sealing member comprises a flat plate having a hole to form said flange portion, and a cylindrical portion that is separate from said flange portion.
 7. A lid of a secondary battery as claimed in claim 6 wherein said cylindrical portion is made of a fluororesin. 